Fix top-level nesting selectors in loaded plain CSS (#2560)

See sass/sass#4055

Author: nex3

Diff for: CHANGELOG.md

@@ -1,3 +1,11 @@
+## 1.87.0
+
+* **Potentially breaking bug fix:** When a plain CSS file with a top-level
+  nesting selector `&` is loaded into a nested Sass context via
+  `meta.load-css()` or `@import`, Sass now emits plain CSS nesting rather than
+  incorrectly combining it with the parent selector using a descendant
+  combinator.
+
 ## 1.86.3
 
 * Fix a bug introduced in 1.86.1 where Sass fails to resolve paths starting with

Diff for: lib/src/ast/selector.dart

@@ -14,6 +14,7 @@ import '../visitor/serialize.dart';
 import 'node.dart';
 import 'selector/complex.dart';
 import 'selector/list.dart';
+import 'selector/parent.dart';
 import 'selector/placeholder.dart';
 import 'selector/pseudo.dart';
 
@@ -49,6 +50,13 @@ abstract base class Selector implements AstNode {
   @internal
   bool get isInvisible => accept(const _IsInvisibleVisitor(includeBogus: true));
 
+  /// Whether this selector contains a [ParentSelector].
+  ///
+  /// @nodoc
+  @internal
+  bool get containsParentSelector =>
+      accept(const _ContainsParentSelectorVisitor());
+
   // Whether this selector would be invisible even if it didn't have bogus
   // combinators.
   ///
@@ -169,7 +177,7 @@ class _IsBogusVisitor with AnySelectorVisitor {
   }
 }
 
-/// The visitor used to implement [Selector.isUseless]
+/// The visitor used to implement [Selector.isUseless].
 class _IsUselessVisitor with AnySelectorVisitor {
   const _IsUselessVisitor();
 
@@ -182,3 +190,10 @@ class _IsUselessVisitor with AnySelectorVisitor {
 
   bool visitPseudoSelector(PseudoSelector pseudo) => pseudo.isBogus;
 }
+
+/// The visitor used to implement [Selector.containsParentSelector].
+class _ContainsParentSelectorVisitor with AnySelectorVisitor {
+  const _ContainsParentSelectorVisitor();
+
+  bool visitParentSelector(ParentSelector _) => true;
+}

Diff for: lib/src/visitor/async_evaluate.dart

@@ -2373,7 +2373,11 @@ final class _EvaluateVisitor
       plainCss: _stylesheet.plainCss,
     );
 
-    var nest = !(_styleRule?.fromPlainCss ?? false);
+    var nest = switch (_styleRule) {
+      null => true,
+      CssStyleRule(fromPlainCss: true) => false,
+      _ => !(_stylesheet.plainCss && parsedSelector.containsParentSelector)
+    };
     if (nest) {
       if (_stylesheet.plainCss) {
         for (var complex in parsedSelector.components) {
@@ -4071,7 +4075,11 @@ final class _EvaluateVisitor
     }
 
     var styleRule = _styleRule;
-    var nest = !(_styleRule?.fromPlainCss ?? false);
+    var nest = switch (_styleRule) {
+      null => true,
+      CssStyleRule(fromPlainCss: true) => false,
+      _ => !(node.fromPlainCss && node.selector.containsParentSelector)
+    };
     var originalSelector = nest
         ? node.selector.nestWithin(
             styleRule?.originalSelector,

Diff for: lib/src/visitor/evaluate.dart

@@ -5,7 +5,7 @@
 // DO NOT EDIT. This file was generated from async_evaluate.dart.
 // See tool/grind/synchronize.dart for details.
 //
-// Checksum: 25aa2d050126950ea37dc1c53539f0b041356e8e
+// Checksum: 607745b48d0737b3be112d0a8753dd87492fcc31
 //
 // ignore_for_file: unused_import
 
@@ -2380,7 +2380,11 @@ final class _EvaluateVisitor
       plainCss: _stylesheet.plainCss,
     );
 
-    var nest = !(_styleRule?.fromPlainCss ?? false);
+    var nest = switch (_styleRule) {
+      null => true,
+      CssStyleRule(fromPlainCss: true) => false,
+      _ => !(_stylesheet.plainCss && parsedSelector.containsParentSelector)
+    };
     if (nest) {
       if (_stylesheet.plainCss) {
         for (var complex in parsedSelector.components) {
@@ -4072,7 +4076,11 @@ final class _EvaluateVisitor
     }
 
     var styleRule = _styleRule;
-    var nest = !(_styleRule?.fromPlainCss ?? false);
+    var nest = switch (_styleRule) {
+      null => true,
+      CssStyleRule(fromPlainCss: true) => false,
+      _ => !(node.fromPlainCss && node.selector.containsParentSelector)
+    };
     var originalSelector = nest
         ? node.selector.nestWithin(
             styleRule?.originalSelector,

Diff for: pkg/sass_api/CHANGELOG.md

@@ -1,4 +1,4 @@
-## 15.3.3
+## 15.4.0
 
 * No user-visible changes.
 

Diff for: pkg/sass_api/pubspec.yaml

@@ -2,15 +2,15 @@ name: sass_api
 # Note: Every time we add a new Sass AST node, we need to bump the *major*
 # version because it's a breaking change for anyone who's implementing the
 # visitor interface(s).
-version: 15.3.3
+version: 15.4.0
 description: Additional APIs for Dart Sass.
 homepage: https://github.com/sass/dart-sass
 
 environment:
   sdk: ">=3.6.0 <4.0.0"
 
 dependencies:
-  sass: 1.86.3
+  sass: 1.87.0
 
 dev_dependencies:
   dartdoc: ^8.0.14

Diff for: pubspec.yaml

@@ -1,5 +1,5 @@
 name: sass
-version: 1.86.3
+version: 1.87.0
 description: A Sass implementation in Dart.
 homepage: https://github.com/sass/dart-sass